This invention relates to the art of measuring body fluid pressure, such as blood pressure, within the cardiovascular system, and, more particularly, to apparatus for directly measuring the body fluid pressure at multiple sites of interest by means of a catheter having a single optical fiber therein with multiple pressure transducers for simultaneously sensing pressure at different sites.
It is known in the art to employ catheter tip transducers insertable into a blood stream for purposes of providing direct pressure monitoring at the location of interest. Many of such catheter tip transducers employ semiconductors and other sensing elements requiring an electrical signal to be carried by wires throughout the length of the catheter from the site of interest to a location externally of the body being tested. Such semiconductor tip transducers require the use of electricity to power the sensor. The use of electricity not only renders the device susceptible to electromagnetic interference, but also introduces the possible hazard of arrhythmia induction.
To overcome some of the noted difficulties, other devices for determining blood pressure in the cardiovascular system have included catheters employing optically based pressure transducers at the distal end. Such devices typically take the form as illustrated and described in U.S. Pat. Nos. 3,249,105 and 3,215,135, to Polyanyi and Franke. Each of these devices employs a catheter having fiber optic means extending the length of the catheter to the distal end thereof at which the fiber optic means is in optical communication with a pressure transducer. However, each of these devices is limited to measuring the pressure at a single site at a time. If pressure readings are required at different sites, then the readings must be taken at different times and the catheter must be moved so that its tip transducer at the distal end is moved from site to site.
It is often desirable to measure intravascular pressure at more than one site, the readings being taken simultaneously. One device known in the prior art capable of performing this function has been disclosed in U.S. Pat. No. 4,543,961 to D. C. Brown, assigned to the same assignee as the present invention. In Brown, supra, there is provided an elongated catheter having a plurality of optical fibers aligned end-to-end in the lumen of the catheter. A plurality of pressure transducers are provided along the length of the catheter with each being associated with the spacing between two aligned optical fibers. The pressure transducer includes a filter-mirror which is movable between the adjacent ends of two spaced apart fibers, the movement being in response to pressure acting against the catheter. Light is directed into the proximal end of the catheter and is transmitted by the optical fibers. At each pressure transducer, light of one wavelength will be reflected by a filter-mirror back to the proximal end in accordance with the pressure exerted on the transducer at that site. Each filter-mirror reflects only one selected color and transmits other colors. Consequently, at the proximal end, the reflected light of three different colors may be individually examined to determine the pressure exerted at each of the three sites under examination.
The present invention is directed to improvements over that disclosed in Brown, supra. The construction in Brown employs a plurality of optical fibers aligned end-to-end within the lumen of an elongated flexible catheter. This results in difficulty of construction, since a typical catheter may have a diameter on the order of 0.06 inches and the optical fiber carried therein may be on the order of 400 micra. Placing a plurality of such fibers in end-to-end alignment along with associated filter-mirrors within such a catheter presents substantial difficulty in manufacture.
The present invention is similar to that discussed in Brown, supra, but permits the use of a single elongated fiber, together with a plurality of pressure transducers associated with the fiber in such a manner that the fiber is not interrupted at the location of each transducer, as in the case of Brown. This is achieved in the present invention by employing pressure transducers based on that described in my previously filed U.S. application Ser. No. 671,913, supra. The transducer disclosed therein is constructed of flexible, optically absorbent material having a portion thereof which makes variable surface area contact with an uncladded core portion of the optical fiber in dependence upon transversely applied pressure forces. The variations in surface contact area cause changes in the light refraction characteristics and this modulates the intensity of light passing through the core proximate thereto. The use of a plurality of such transducers located at spaced apart locations on an elongated single optical fiber achieves a multiple site fiber optic pressure transducer system which is easier to manufacture and has a faster frequency response than that of the prior art discussed hereinabove.